DHAKA, July 7 -- In a first-ever terror attack on Eid congregation, at least two constables and an attacker were killed and 11 others injured on Thursday morning at the entrance of Sholakia Eid prayer venue in Kishoreganj district, some 117 km northeast of Dhaka.

Witnesses described hearing several explosions and subsequently exchange huge of gunfire between police and attackers at around 9:30 a.m. local time at the scene, where the largest congregation of prayer in Bangladesh is held on the occasion of Eid ul-Fitr that marks the end of the Muslims' holy fasting month of Ramadan.

Such an attack on Eid day is said to be first time in Bangladesh. It was not known immediately who launched the attack.

A police official told Xinhua from Kishorganj that security measures have been beefed up after the incidents of bomb explosions and gun fire in which two police constables and a gunmen whose identity was not known yet were killed, and 11 people including at least six policemen were injured.

"We're closely monitoring the situation," said the official who declined to be named.

Two attackers have been detained with bullet wounds.

It was not known immediately whether there were any other attackers .

The incident came about a week after terror attack in a restaurant in Dhaka's diplomatic enclave Gulshan in which 22 people including 18 foreigners and two policemen were killed.